Cases of Fatal Brain Disease Showing Up Decades After Infection

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A few hundred people around the world caught a rare and fatal
brain disease from contaminated growth hormone treatments they
received during the 1950s through 1980s. Now, although use of the
contaminated hormone stopped decades ago, scientists say they
continue to see new cases of the brain disease today, up to 40
years after the patients were exposed, according to a new study.

The
study describes 22 new cases of the brain disease, called
Creutzfeldt-Jakob disease, that were diagnosed in people in the
United Kingdom between 2003 and 2014. All of the patients had a
growth hormone deficiency as children, and had been treated with
growth hormone taken from cadavers — a practice that was stopped
in 1985 when scientists realized some batches of the growth
hormone were contaminated with prions, the infectious proteins
that cause
Creutzfeldt-Jakob disease (CJD).

"We know that prion diseases can have an enormously long
incubation period," said Dr. Peter Rudge, a co-author of the new
study and a consultant neurologist at the National Prion Clinic
in London. "Ultimately, the disease will die out, but it is
impossible to predict when," Rudge told Live Science. [ 10
Things You Didn't Know About the Brain ]

The patients in the new study started to show symptoms of CJD
about 20 to 40 years after they were treated with the hormone.
Hand tremors and an unsteady gait were common first symptoms of
the condition, and some patients experienced limb pain, dizziness
or daytime sleepiness, the researchers said.

Once patients showed symptoms of the disease, their condition
usually deteriorated quickly — on average, patients lived only
about 14 months after first showing symptoms, the researchers
said.

Researchers are uncertain when they will see the last of the CJD
cases tied to the
growth hormone treatments.

A total of 77 people in the United Kingdom have developed CJD
since 1985, and there have been additional cases in other
countries that used growth hormone from cadavers, including the
United States, France and Australia.

The new study also suggests that all of the patients in the
United Kingdom became ill from a single person who had CJD and
donated tissue after his or her death to be used in growth
hormone treatments. Humans naturally have prions, however, so
when people become infected with a "bad" or abnormal prion, the
abnormal prion can cause changes in a person's natural prion
proteins, leading to a buildup of abnormal prions in the brain,
which causes disease.

Researchers think that certain people who are exposed to the
abnormal proteins become sick more quickly: those whose natural
prion gene matches that of the infecting prion at a specific
point in the gene.

In the United Kingdom, most of the people who became ill early on
had a genotype known as VV, and the researchers think the reason
for this is that the tissue donor also had this genotype. "We
know from human and animal work that compatibility between donor
and recipient shortens incubation period," Rudge said.

It wasn't until more recently that researchers started to see
more people get sick who had a different genotype — called MV or
MM. In fact, among the 22 new cases, 17 people had the MV
genotype, four had the MM genotype and just one had the VV
genotype.

The researchers think that over time, the body may gradually
produce prions that "match" the infectious prion, and once this
happens, the disease can take hold.

The findings may have implications for cases of mad cow disease,
known as
variant Creutzfeldt-Jakob disease (vCJD) in people, which is
also caused by prions and is tied to eating contaminated beef in
the United Kingdom.

So far, all the people who have developed vCJD have had the MM
genotype, leading some researchers to suspect that the infectious
prions that cause vCJD can only sicken the people who have this
genotype, Rudge said.

However, the new study suggests it's possible that people with
other genotypes may yet become sick with vCJD. If people with
other genotypes have a longer incubation period of the disease
than the people sickened to date, "there is a risk that a second
epidemic of vCJD could occur," in people who ate tainted beef,
Rudge said.

"Furthermore, it is possible that many people are incubating this
disease," without knowing it, he said.